Smoking and risk of incident psoriatic arthritis in US women

Objectives Psoriatic arthritis (PsA) is an inflammatory arthritis that is associated with psoriasis. Previous studies have found an association between smoking and psoriasis, but the association with PsA is unclear. The authors aimed to evaluate the association between smoking and the risk of incident PsA in a large cohort of women. Methods 94 874 participants were included from the Nurses' Health Study II over a 14-year period (1991-2005). Information on smoking was collected biennially during follow-up. The incidence of clinician-diagnosed PsA was ascertained and confirmed by self-reported questionnaires. Results During 1 303 970 person-years' follow-up, the authors identified 157 incident PsA cases. Among total participants, smoking was associated with an elevated risk of incident PsA. Compared with never smokers, the RR was 1.54 for past smokers (95% CI 1.06 to 2.24) and 3.13 for current smokers (95% CI 2.08 to 4.71). With increasing smoking duration or pack-years, the risk of PsA increased monotonically (p for trend <0.0001). The increase in risk was particularly significant for PsA cases with more severe phenotypes. Secondary analysis among participants developing psoriasis during the follow-up replicated the association, demonstrating an increased risk of PsA among psoriasis cases. The risk was significant for those with higher cumulative measures of smoking or PsA cases with more severe phenotypes. Conclusion In this study smoking was found to be associated with a risk of PsA and cumulative measures of smoking were also associated with a higher risk of PsA among women.